The present invention is related to a novel process for preparing certain piperidine derivatives which are useful as antihistamines, antiallergy agents and bronchodilators [U.S. Pat. No. 4,254,129, Mar. 3, 1981, U.S. Pat. No. 4,254,130, Mar. 3, 1981 and U.S. Pat. No. 4,285,958, Apr. 25, 1981].
These piperidine derivatives can be described by the following formulas: ##STR1## wherein R.sub.1 represents hydrogen or hydroxy;
R.sub.2 represents hydrogen; or PA1 R.sub.1 and R.sub.2 taken together form a second bond between the carbon atoms bearing R.sub.1 and R.sub.2 ; PA1 n is an integer of from 1 to 5; PA1 R.sub.3 is --CH.sub.2 OH, --COOH or --COOalkyl wherein the alkyl moiety has from 1 to 6 carbon atoms and is straight or branched; PA1 each of A is hydrogen or hydroxy; and PA1 pharmaceutically acceptable salts, hydrates and individual optical isomers thereof. PA1 R.sub.2 represents hydrogen; or PA1 R.sub.1 and R.sub.2 taken together form a second bond between the carbon atoms bearing R.sub.1 and R.sub.2 ; PA1 n is an integer of from 1 to 5; PA1 R.sub.3 is --CH.sub.2 OH, --COOH or --COOalkyl wherein the alkyl moiety has from 1 to 6 carbon atoms and is straight or branched; PA1 each of A is hydrogen or hydroxy; and PA1 pharmaceutically acceptable salts, hydrates and individual optical isomers thereof comprising the steps of: PA1 D=hydrogen or a suitable protecting group PA1 R.sub.1 ' and R.sub.2 '=hydrogen, protected hydroxy, hydroxy or taken togther to form a second bond between the carbon atoms bearing R.sub.1 ' and R.sub.2 ' PA1 R=C.sub.1 -C.sub.6 alkyl or hydrogen
The novel process for preparing the piperidine derivatives of formula (I) and formula (II) of the present invention offers high yields and ease of purification.